Need tuning advice.

I need tuneing advice. My vf39 is on its last leg, it burns a quart of oil about every 500 miles...about once a week. I am replacing the vf39 this weekend with a very slightly used VF48, out of a 2012 sti, along with an upgraded compressor wheel (which is said to flow up to 15% more). If I am to go back to get it re tuned on a dyno, it is going to cost me 500 dollars and a drive from San Diego to Los Angeles (and a full day off of work). There are a few tuners in San Diego that will do a street tune for 250 dollars, just running it down the street. I would save 250 dollars plus a full days work gas and time if I did a local street tune. My question is do I need a complete tune, or can a street tune with minor adustments be fine?

I also plan on installing a grimspeed 3 port solenoid before either tune.

Do you have a WBO2? If not, invest in one now and a street tune will be just as good as a dyno tune (and in some ways better).

Difficult to judge since IHI does not publish compressor maps, but the VF48 should be nearly identical to the VF39. I am also HIGHLY skeptical about this "rebuilt" VF48 since IHI has never released a rebuild kit... who rebuilt the turbo? Is it the stock CHRA?

The VF48 is not rebuilt. It has appoximitly 6000 miles on it. All I did to the turbo was install an upgraded billet compressor wheel. A turbo shop here in San Diego called Action Turbo(a repitable shop) said they have used the wheels before, and they come pre balanced. I put the wheel in myself, and it works fine.

Question? when tuning, does the factory o2 sensor read as a wideband?...I thought they made a kit that can hook to the factory o2 sensor? so that would mean the tuner can read fuel ratios when tuneing with his computer, on a street tune, correct? or am I wrong?

Originally Posted by zax

Do you have a WBO2? If not, invest in one now and a street tune will be just as good as a dyno tune (and in some ways better).

Difficult to judge since IHI does not publish compressor maps, but the VF48 should be nearly identical to the VF39. I am also HIGHLY skeptical about this "rebuilt" VF48 since IHI has never released a rebuild kit... who rebuilt the turbo? Is it the stock CHRA?

The VF48 is not rebuilt. It has appoximitly 6000 miles on it. All I did to the turbo was install an upgraded billet compressor wheel. A turbo shop here in San Diego called Action Turbo(a repitable shop) said they have used the wheels before, and they come pre balanced. I put the wheel in myself, and it works fine.

... Still skeptical

Originally Posted by ronzonothebugeye

Question? when tuning, does the factory o2 sensor read as a wideband?...I thought they made a kit that can hook to the factory o2 sensor? so that would mean the tuner can read fuel ratios when tuneing with his computer, on a street tune, correct? or am I wrong?

Not to sound condescending, but yes, you are wrong. The front O2 sensor actually is a zirconia WBO2 sensor, but the ECU cannot use this sensor as a WBO2 sensor. Even WBO2 sensors will change sensor scaling as the ambient pressure changes. The exhaust gas pressure pre-turbo can actually rise as high as 50 PSI, which makes any reading (besides a rich/lean assessment) useless. As such, the ECU registers the rich and lean condition in cyclic fueling logic -- if lean, then increase pulse width; if rich then decrease pulse width. With an NA car, precisely what you have stated could be performed, but not with the WRX. Unfortunately the rear O2 sensor is a standard zirconia narrow-band O2 sensor with the primary purpose of monitoring catalyst efficiency. Dyno tunes can be performed using a full EGA (exhaust gas analyzer) and are extremely flexible, also monitoring NOx emissions which are useful in judgement of EGTs.

Everything I've stated above applies to GD WRXs. As an interesting side-note, both EJ257 and Heide264 have informed me that the logic in the newer CANbus ECUs actually utilizes a component of the rear O2 sensor readings to establish closed-loop control of the AFRs. Given this information, I do wonder if the rear O2 sensor on the CANbus WRXs actually is a WBO2 sensor. Anyone want to chime in or look up part numbers?

EDIT:
Here is something that helped me quite a bit to understand the hardware difference between a WBO2 and a narrow-band Oxygen sensor (pictures taken from Wikipedia):

Not to sound condescending, but yes, you are wrong. The front O2 sensor actually is a zirconia WBO2 sensor, but the ECU cannot use this sensor as a WBO2 sensor. Even WBO2 sensors will change sensor scaling as the ambient pressure changes. The exhaust gas pressure pre-turbo can actually rise as high as 50 PSI, which makes any reading (besides a rich/lean assessment) useless. As such, the ECU registers the rich and lean condition in cyclic fueling logic -- if lean, then increase pulse width; if rich then decrease pulse width. With an NA car, precisely what you have stated could be performed, but not with the WRX. Unfortunately the rear O2 sensor is a standard zirconia narrow-band O2 sensor with the primary purpose of monitoring catalyst efficiency. Dyno tunes can be performed using a full EGA (exhaust gas analyzer) and are extremely flexible, also monitoring NOx emissions which are useful in judgement of EGTs.

Everything I've stated above applies to GD WRXs. As an interesting side-note, both EJ257 and Heide264 have informed me that the logic in the newer CANbus ECUs actually utilizes a component of the rear O2 sensor readings to establish closed-loop control of the AFRs. Given this information, I do wonder if the rear O2 sensor on the CANbus WRXs actually is a WBO2 sensor. Anyone want to chime in or look up part numbers?

Not condesending at all, I appriciate the information. I'm on a budget just like everyone else, so pulling more money from wife is going to be hard...lol. Im probably not going to buy the 3 port boost solenoid which I was planning to buy, and instead I'm going to buy a wideband o2sensor and gauge. Do you think the stock boost solenoid is sufficaint, or does the 3 port solenoid really make a big differnece?

Not condesending at all, I appriciate the information. I'm on a budget just like everyone else, so pulling more money from wife is going to be hard...lol. Im probably not going to buy the 3 port boost solenoid which I was planning to buy, and instead I'm going to buy a wideband o2sensor and gauge. Do you think the stock boost solenoid is sufficaint, or does the 3 port solenoid really make a big differnece?

hahaha...your right...I'm just impatient, I put the turbo in on Sunday, and I want to boost already. Ive been driving it, and I punched it once....feels about the same as the vf39, not sure if the vf48 is even any differnet....

As an interesting side-note, both EJ257 and Heide264 have informed me that the logic in the newer CANbus ECUs actually utilizes a component of the rear O2 sensor readings to establish closed-loop control of the AFRs. Given this information, I do wonder if the rear O2 sensor on the CANbus WRXs actually is a WBO2 sensor. Anyone want to chime in or look up part numbers?

All 32-bit ECUs (including the '06/'07 WRX will have fueling issues without the presence of a rear O2 sensor).

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